The rest-frame transition frequencies of the $6s{}^2{S}_{1/2}\to 6p{}^2{P}_{1/2}$ ($D_1$) and $6s{}^2{S}_{1/2}\to 6p{}^2{P}_{3/2}$ ($D_2$) lines in the stable isotopes of ${\mathrm{Ba}}^{+}$ were measured with an accuracy better than $200\mathrm{kHz}$ through (quasi)simultaneous collinear and anticollinear laser spectroscopy, leading to an improvement in the accuracy of the isotope shifts by more than an order of magnitude compared to previous data. The ratio of the field-shift constants in the $D_1$, $D_2$ fine-structure doublet has been determined to $f=1.0186\left(9\right)$ through a King plot analysis. These collinear laser spectroscopy measurements have reached an accuracy comparable to ion-trap measurements on allowed dipole transitions. Our result provides an accurate benchmark for atomic many-body calculations and is compared to pure Dirac-Hartree-Fock calculations and to elaborate multiconfigurational Dirac-Fock calculations. The influence of correlation effects and the Breit interaction on the isotope shift in ${\mathrm{Ba}}^{+}$ are discussed.

• Received 7 November 2018

DOI:https://doi.org/10.1103/PhysRevA.99.012511